During the cataract operation, the body's own natural lens of a patient's eye, in which a cataract has developed, is replaced with an artificial lens, a so-called intraocular lens. An opening into the capsular bag is prepared within the inner edge of the iris by means of an incision through the sclera or cornea. The natural lens is then shattered with an ultrasonic instrument through this opening and is then removed. After the natural lens has been removed, the intraocular lens is introduced through the opening in the capsular bag of the patient's eye.
Intraocular lenses with a spherical, aspherical, multifocal and also a toric geometry are used, in particular, in eye surgery. In the case of toric intraocular lenses, it is necessary, in order to compensate for patients' visual defects, for the axis of the torus of the intraocular lens to be oriented in a defined manner in the patient's eye during the cataract operation.
During the cataract operation, the surgeon is faced with the problem that the patient's eye can move during an operation even with local anesthesia. The image of the object area that is presented to a surgeon during a cataract operation is therefore not stationary.
Therefore, in order to indicate the azimuthal orientation of the patient's eye to a surgeon in an operation, the patient's eye is often provided with a mark, which indicates a direction, before the operation.
DE 10 2009 030 504 A1 describes an eye surgery microscopy system of the type mentioned at the outset, in which the azimuthal orientation of a patient's eye provided with a mark can be automatically detected. This eye surgery microscopy system has imaging optics for generating the image of an object plane. It contains an electronic image sensor which receives the image of the object plane. The eye surgery microscopy system has a computer unit which is connected to the image sensor. The computer unit can be used to calculate the position of the center of the limbus or of the iris of a patient's eye. For this purpose, the computer unit contains a computer program which determines the azimuthal orientation of a patient's eye provided with a mark by means of correlation with a reference image.
DE 10 2009 052 128 A1 discloses an eye surgery microscopy system containing a measuring device which can be used to determine an axis of the astigmatism of a patient's eye in an ophthalmological operation. In this eye surgery microscopy system, a determined axis of the astigmatism can be displayed in a manner superimposed on the observation image of the patient's eye.
U.S. Pat. No. 5,865,832 discloses an eye surgery microscopy system containing imaging optics which are automatically corrected when a patient's eye moves. For this purpose, the imaging optics are connected to a device for detecting the position of the patient's eye. This device contains an image sensor which is used to continuously capture the patient's eye in order to correct the imaging optics on the basis of a change in the image captured with the image sensor.
U.S. Pat. No. 6,866,661 B2 describes a device for calculating the change in orientation of a patient's eye in an eye surgery system for laser in-situ keratomileusis. In this device, the patient's eye is continuously captured with an image sensor. The continuously captured images are subjected to image evaluation therein. During this image evaluation, characteristic structures of the patient's eye, for example blood vessels of the sclera, are then determined in order to calculate the change in the orientation of the patient's eye from the locations of these structures in the continuously captured images.
United States patent application publication 2005/0270486 discloses an eye tracking system and a method for determining a position of an eye or a part of an eye in an image of an image sequence by performing a comparison between said image and a reference image. This method includes aligning a set of images and computing an enhanced reference image based on a combination of the set of aligned images. The position in said image of the image sequence is determined by comparing the image of the image sequence to the enhanced reference image to yield a motion estimation between the reference image and the image of the image sequence.